The present invention relates generally to a hitch assembly for a tractor or similar work vehicle. More particularly, the invention relates to a hitch assembly adapted for installation as original equipment on vehicles such as tractors, or as a retrofit on vehicles originally outfitted with only a drawbar or with no draft structure. The assembly may be used as a fully or semi-mounted hitch and has a greatly simplified and accessible structure as compared to conventional hitch assemblies, reducing the number of parts and the weight of the hitch assembly and facilitating mounting and servicing of the hitch components.
In the art of hitch assemblies for tractors and other work vehicles, a variety of structures have been proposed and are currently in use. Conventional hitch assemblies typically include a rocker assembly for raising and lowering an implement coupled to the hitch, one or more hydraulic cylinders connected to the rocker assembly and a pair of draft links for mounting and pulling an implement. Such hitches also commonly include a third or upper link that cooperates with the rocker assembly and draft links to maintain a desired orientation of the implement.
The rocker assembly of conventional tractor hitches typically includes a rockshaft splined to receive rocker arms as well as a bell crank or lever for rotating the rockshaft in response to extension and retraction of a hydraulic cylinder. The rockshaft is supported on journal bearings either inboard or outboard of the rocker arms. For rear-mounted hitches, the rockshaft journal bearings are typically provided in a massive support casting secured to the upper, rear or side surfaces of the differential housing. For raising and lowering the hitch either a single or a pair of lift cylinders may be provided. Where a single lift cylinder is used, the cylinder is generally located within the differential housing and cooperates with a central bell crank or lever splined to the rockshaft. Where two lift cylinders are present, the cylinders are typically external to the differential housing and are mounted on either side of the tractor rear differential. In both cases the rocker arms are connected to the draft links via lift links including turn buckles and are raised and lowered by rotation of the rockshaft and rocker arms. Hitch assemblies generally of this type are described in U.S. Pat. No. 3,399,733, issued to North on Sep. 3, 1968, U.S. Pat. No. 3,994,347, issued to Schowalter on Nov. 30, 1976, U.S. Pat. No. 4,470,613, issued to Sykes on Sep. 11, 1984 and U.S. Pat. No. 4,862,971, issued to Azzarello et at. on Sep. 5, 1989.
While conventional tractor hitches of the type described above have provided a useful and reliable tool for positioning and manipulating implements, they are not without drawbacks. A first significant drawback with such conventional hitch assemblies is the difficulty of servicing the hitch components, particularly the rocker assembly and lift cylinders. Where a lift cylinder is located in the rear differential housing, routine septicing of the cylinder, such as for replacement of worn seals, requires removal of the hitch support casting and partial dismantling of the differential. Similarly, for both internal and external cylinder designs, servicing of the rockshaft bearings, bearing seals or the rockshaft itself requires dismantling of the rocker assembly.
Another important drawback of conventional hitch designs stems from the size, weight and complexity of the hitch support structure. Where a hitch is installed as original equipment on a vehicle, this support structure may be simplified to some extent by integrating portions into the differential housing structure. However, to provide the flexibility to retrofit vehicles not originally equipped with a hitch and to reduce the cost of vehicles on which a hitch is not required, a number of schemes have been devised for attaching an add-on support structure to the tractor frame, typically by bolting one or more support castings to the differential housing. Moreover, certain known designs incorporate several additional features into a single add-on support casting, such as a power take off (PTO) and drawbar. While this add-on approach to hitch design provides a degree of flexibility for the vehicle owner, known add-on hitch assemblies include massive cast metal supports, typically weighing several hundred pounds. The size and weight of these supports not only render the hitch difficult to mount, but often require special handling equipment and several service personnel to remove and replace, thereby reducing the field serviceability of the hitch. In addition, where several features are included in a single add-on support, the vehicle owner may have to remove the hitch or one of the other features from service during repair or servicing of the support or the components of a single feature.
The present invention features a novel hitch assembly that can be installed as original equipment on a tractor or other work vehicle, or that can be easily field retrofitted the need for dismantling of the differential or other systems on the vehicle. The hitch assembly comprises a simple structure including relatively light weight supports that may be field mounted and removed when necessary. The entire assembly remains completely accessible when installed and is preferably independent of other operating features of the vehicle, thus greatly facilitating servicing. In a particularly preferred configuration, the rocker and attachment supports are designed to provide an extremely advantageous geometry for transmitting forces on the rocker, the hitch links and the lift cylinders to the attachment structure and the tractor frame.